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Equine obesity

If there is any truth to the idea that after a while owners start to look like their pets, then many horsemen and women need to go on a diet.

The general equine population of the United States is working less, eating more and becoming fat.

Horses need exercise, but that can vary from structured, intense exercise such as these horses about to begin a 50-mile endurance ride, to an easy trail ride or simple daily walk.

Advances in nutrition and in pasture management over the years have led to better-fed horses and clients have been educated about equine dental care, appropriate deworming programs and other aspects of good husbandry that make it easier for horses to get fat and stay that way.

Education needed
This does not mean that we are treating horses too well, only that more education needs to be done.

Veterinarians should make clients aware of the problems associated with obesity in horses and encourage them to make a distinction between fat and fit.

This topic is especially important as summer approaches bringing with it lush, green, "carbohydrate-loaded" grass and the potential for overweight horses to, nutritionally, go overboard.

Obesity disease link
Many new studies are linking obesity to a variety of disease conditions in horses.

Dr. Philip Johnson, professor of equine internal medicine at the University of Missouri College of Veterinary Medicine, has been investigating the links between obesity and laminitis.

In this "politically correct" era, whether you call them "vertically challenged" or "full-figured", a fat horse is not difficult to identify. This horse shows the typical cresty neck, lack of rib or body definition and deep back and rump furrows seen in the overweight horse. One of the most difficult aspects of dealing with these horses is convincing owners that overfeeding is not healthy. Many owners equate equine food with care and concern and feel that a fat horse is a happy one.

Johnson is especially interested in the possible association between laminitis and the medical condition known as glucose intolerance or insulin resistance. This condition is similar to the early stages of what, in humans, will become Type II or adult onset diabetes.

Many veterinary researchers now feel that a similar condition exists in horses and that obesity is strongly related.

"Obese horses and ponies with laminitis are also commonly affected with insulin resistance," noted Johnson, and current studies are attempting to determine which condition comes first. Do horses become obese because of insulin resistance and do vascular changes due to obesity then cause laminitis? Or can the increased levels of insulin (hyperinsulinemia) seen as the horse's body responds to insulin resistance cause or potentiate obesity and also be a primary factor in the development of laminitis? These are very active areas of current study and the preliminary information is leading to many more questions than answers so far.

Laminitis
Drs. Donaldson, Jorgenson and Beech from the New Bolton Center at the University of Pennsylvania School of Veterinary Medicine, recently looked at a number of horses that had laminitis. They were looking at the association of impaired pituitary function in horses with laminitis, but they also noted that a number of horses in their study had no pituitary dysfunction but did have hyperinsulinemia.

"Because most of these horses were overweight," say Donaldson, Jorgenson and Beech, "it is possible that hyperinsulinemia was associated with obesity."

These researchers then went on to state that "alterations in glucose metabolism (such as insulin resistance) have been implicated in the pathogenesis of laminitis."

They noted that obese humans with insulin resistance have abnormal activity of 11 B-hydroxysteroid dehydrogenase-1 (11B-hsd1) which is an enzyme that activates cortisol. This enzyme is also believed to be abnormal in horses with laminitis.

One horse in their study had a high insulin concentration, hyperglycemia, a cresty neck and a body score of 8/9. This horse was treated with dietary restriction, phenylbutazone and corrective trimming.

After four months of consistent treatment/management, the horse's body weight had decreased by 14 percent, insulin and glucose concentrations were within normal range, body score was 5/9 and the horse was now sound.

While this is just one example, it does suggest the possibility that obesity itself is a potential cause or factor in some of the most difficult diseases of horses and that treating obesity may be as important as any other treatments that veterinarians can offer.

Efficiency loss
Laminitis and insulin resistance are not the only conditions that are being linked to obesity.

Overweight horses are less efficient athletes.

This may sound immediately obvious but is not being appreciated by some owners and trainers. Some horsemen and women like to see fully rounded horses in the show ring. This would be good if that appearance was due to fit muscle, but too often overfeeding is replacing adequate conditioning.